Effects of salt-loading hypertension on nociception in rats

Ayobami Oladele Afolabi,¹ Saheed Kolade Mudashiru,¹ Isiaka Abdullateef Alagbonsi<sup>2

1</sup>Department of Physiology, College of Health Sciences, Ladoke Akintola University of Technology, Ogbomoso, Oyo, Nigeria; ²Department of Physiology, Faculty of Medicine, Kogi State University, PMB 1008, Anyigba, Kogi, Nigeria

Background: There is on going controversy on the effect of experimentally induced hypertension on nociception. The effect of salt-loading-induced hypertension on pain was studied in male rats.
Method: Twenty-four male Sprague-Dawley rats (160–280 g) were divided into two groups. Group A (n = 12) was treated with normal-feed diet (control), while group B (n = 12) was treated with 8% salt-loaded diet for 10 weeks. After 10 weeks of the treatment, six rats each from groups A and B were used for blood pressure measurement, while the remaining six rats were used for both the tail-flick and formalin tests. Thermal and chemical pain test were assessed using tail immersion test (tail flick) and formalin test pain paradigms at onset of salt-loading diet and after 10 weeks of salt loading.
Results: Chronic administration of salt-loading diet caused significant increases (P < 0.001) in systolic blood pressure, diastolic blood pressure, and mean arterial blood pressure. Moreover, salt-loading-induced hypertension was found to significantly reduce pain sensitivity in the tail-immersion test (P < 0.001) and in the early and late phase of the formalin test (P < 0.01). However, the hypoalgesia was higher in the late phase (94.8%) than in the early phase (56.8%) of the formalin test.
Conclusion: The present study suggests that high salt-loading-induced hypertension causes hypoalgesia in rats, which might be due more to reduction in inflammatory response.

Keywords: formalin test, tail-flick test